Normal visual input is indispensable to the development and maintenance of visual centers. Abnormal input to one eye achieved by lid-suture induces changes in this deprived eye as well as in visual centers connected with it. For such types of experiments albino rats were believed to be especially suited because of the high percentage (95 percent) of crossed optic fibers. In this species. however, monocular deprivation induced changes in the undeprived functional eye and relevant optic centers and prevents its use as a control for the deprived side. This damaging effect of light was an obviously disturbing factor in albino rat experiments aimed at studying the morphological consequences of visual deprivation. Inasmuch as this change concerns the visual receptors and its magnitude is related to the length of daily light exposure, enhanced stimulation of the functional eye resulting in damage of the receptors had to be anticipated. In order to eliminate this in the proposed experiments hooded rats will be used, in which the pigmented iris and chorioidea reduce the amount of light entering the eye to a level that is non-injurious to the receptors. The functional eye should then be an adequate control for the companion occluded eye. In hooded rats the visual input is not lateralized, because of the higher proportion of uncrossed fibers as compared to the albino variety. However, the circumscribed location of the contra- and ipsilateral projections in the lateral geniculate as well as in the visual cortex will make it possible to compare the effect of unilateral deprivation on the monocular and binocular segments of the visual cortex. The extent of recovery from morphological changes induced by deprivation after unobstructed vision is restored should provide a morphological correlate to the partially recovered functions described in electro-physiological as well as behavioral experiments.